Roband Varex psu 30-2 Twin help needed

[maninashed]

Does anyone have any service information on this series of high quality PSU's? It's a nice unit and I would like to get this back in full working order. I have 33V at the output, but there is no regulation. There are two channels which are seperate on two PCB's, both appear to be faulty. A service manual would be the icing on the cake but any info would be appreciated.

Bill

[Alistair D]

Looking at the picture some of the voltage feedback links seem to be missing. On each column of 4mm plugs amp + needs to be joined to output +. Likewise amp - needs to be joined output -.

Al

[maninashed]

Thanks Alistair, I've got no user manual either so working blind. So, if I've understood that correctly, there should be links between the AMP+ and output+ and between AMP- and output-on both seperate channels?

Bill

[Alistair D]

Bill,
Do a search on here re Roband. I posted a copy of the manual for more powerful versions of this power supply. I am not sure if the circuit details are applicable but the basic operational concepts apply.

If this is not available PM me your email address. I will send you a copy of the PDF.

Al

[maninashed]

Alistair, thanks I've found the manual you posted. I'll have a good look at the unit tomorrow and post my findings. If anyone else has anything on this unit, please let me know.
Bill

[Pamphonica]

Here's the manual I have which covers the whole range.
- Jeremy

[maninashed]

Thanks Jeremy much appreciated.
Bill

[AC/HL]

It's for remote sensing, to remove inaccuracies caused by lead resistance. Not usually required in low current applications so they can be strapped on the PSU.
Shows good design though.

[maninashed]

Ok, thanks gents. Ive sorted it. On one channel MR14 was s/c, it broke into bits when I touched it and the pcb track was burnt and o/c on the reverse. MR14 is not on the schematic or the component list, so I had to fit the pieces together to read 1N4003. A new one and the track repaired restored operation.
On channel 2 R43 had burned and had been replaced by 2 oversize components, these were replaced with the correct 10R WW and the track repaired. VT5 was o/c, its a dual transistor with 6 leadouts, a 2C444. I had no chance of a relacement, a quick google revealed its parameters. So a quick sift through spares produced 2 BC107s. I fitted these back-to-back but isolated from one another (can is at collector potential). I checked the collector voltage under load/no load which was a max of 5v. Everything seems to be working fine now with good regulation. So I'll give it a long test and see how it goes. If anyone can suggest a more suitable replacement for VT5, Im open to suggestions.
Bill

[Refugee]

Almost any dual transistor with an HFE of 100 0r (or) so will do.
The important thing it the thermal contact between the two transistors.
It will allow small changes in output to occur that will be effected by heat.

[maninashed]

Yes I'm aware of that, if the cans were isolated I would just join them with some copper foil. I haven't got any dual transistors, I've merely substituted the BC107s to prove the fault. As soon as I can get a suitable replacement I'll fit it.
Bill

[woodchips]

A round of applause to Jeremy for posting the circuits. Bob

[Alistair D]

Just to keep the record straight. The PDF that Jeremy posted is a copy of the document I created and posted back in April. It was created from a series of 30 odd JPEGs supplied to me by forum member Ben. The real credit belongs to him.

Woodchips, The two Varex 60-5 supplies you donated to me are now fully refurbished and take pride of place on my workbench.

Thanks
Al

[maninashed]

Can I just thank you both, for responding AND for posting the manual. Its working fine now and as soon as I can get a suitable double transistor, it will be back to its correct order.
Thanks
Bill

[BobGreen]

Hello, I was part of the Roband design team all those years ago so let me know if I can help any time.

[AC/HL]

Originally Posted by woodchips

A round of applause to Jeremy for posting the circuits. Bob

Seconded, if they can be posted it potentially helps us all if they are

[maninashed]

That's interesting Bob, I have to say it is a very nice design, and easy to work on too. The pcbs fold down on spring hinges and can be pulled clear to work on without unsoldering any wires. Aesthetically its a nice thing and would have looked cutting edge in its day. I just wish those dual transistors were more easily available.
Bill

[BobGreen]

Thanks Bill, those were halcyon days at Roband. The main contributor to the Varex project was Keith Billings and also Roy Strand (my mentors then). We had all worked together in MoD and migrated to Roband one by one. Keith went to Canada and wrote books for McGraw Hill available on Amazon such as Switchmode Power Supply Handbook.
73 Bob

[Superhet Si]

Bob, when did you leave Roband?
I started in 1994..

[BobGreen]

I left in about 1968 so must have been a lot different when you got there. I imagine Mr Gold Snr had retired and Andrew was in charge then?